Electrode for devices for varying electrical resistance.



W. G. HUDSON. ELECTRODE FOR DEVICES FOR VARYING ELECTRICAL RESISTANCEAPPLICATION FILED FEB. 19, 1914.

6 1 9 1 1L 1 VJ M u W e m P LI I I.

WALTER, G. HUDSON, OF NEW YORK, N. Y., ASSIGNOR TO RADIO TELEPHONE &TELEGRAPH COMPANY, A CORPORATION 01E DELAWARE.

ELECTRODE FOR DEVICES FOR VARYING ELECTRICAL RESISTAN Specification ofLetters Patent.

Patented July ii, rare.

Application filed February 19, 1914. Serial No. 819,648.

To all whom it may concern: I

Be it known that I, WALTER G. HUDSON, of New York, in the county of NewYork, and in the State of New York, have invented 5 a certain new anduseful Improvement in Electrodes for Devices for Var ing vElectricalResistance, and do hereby declare that the following is a full,clear,'and exact description thereof. The object of my invention hasbeen to provide an improved electrode for use in ceiver, or to increasetheir audibilit-y in tel-' ephony; and to such ends my inventionconsists in the electrode for use in devices for varying electricalresistance hereinafter specified.

In the accompanying drawing the figure is an elevation of an electrodeembodying my invention.

I have chosen as an illustration of my invention that embodiment thereofwhich is the best embodiment knownto me, but

my invention is capable of embodiment in many different forms, and foruse for many difi'erent purposes, and the illustrated embodiment thereofis to be regarded, therefore, as typical only of many possible em- 40bodiments and my invention is 'not to be confined thereto.

The illustrated embodiment of my invention is an electrode for use inthe type of detectors for radio telegraphy or telephony 415 known as asdetectors like the Fleming valve an A ion, and in current amplifiersoperating on similar principles.

These devices make use of two or more electrodes inclosed in a bulb,like an incandescent light bulb, connections with the electrodes beingprovided by means of wires 'sealed in the glass. One or more of theseelectrodes is commonly a lamp filament heated to bring about a change inthe gaseous medium between it and another elec- -and not seeking tocurrents are able to materially afiect its retrode or electrodes, suchthat the said medrum Wlll modify, rectify, amplify, or otherwise conductfeeble, oscillatlng, pulsating, or other currents in such a manner as tomake the same perceptible to a signaling device, such as, for instance,a telephone receiver. I have used the term varying resistance as ageneric term to include such actions as modifying, rectifying,amplifying, or otherwise conducting in a variable manner theoscillating, pulsating or other var able currents, or, under theirinfluence, of supplemental currents provided by local means. In theoperation of the said devices the heated electrode performs twofunctions, namely, that of heating the electrode or filament (if it bein the form of a filament) and that of varying the resistance of themedium between the electrodes. I have discovered that by separatingthese functions,

perform them both by the same substance, I can get improved results, forI find substances which are best adapted to perform one function are notthe substances which are best to perform the other function.

I will state a theory which I believe to be correct, but which I onlyoffer as possibly throwing light on the invention, and I am not -,to bebound by the correctness or incorrectness of the said theory. Suchtheory is as follows: When the filament electrode is heated by means ofan ordinary electric current (for instance, from a small storage abattery) it ionizes and renders sensitively conducting the attenuatedgas between and around all the electrodes within the bulb. When thenegative pole of a second battery, otherwise properly connected with thesys tem, is brought into. electrical connection with the heated filamentelectrode, the latter also throws ofl' ions, greatly adding 'to thesensitiveness of the gaseous medium; so that very'feeble oscillating,pulsating or other sistance to the current from the second battery, andthus cause signals in ordinary signaling devices they would otherwise beunable to operate.

The part of the above theory which is pertinent to my invention is this:1st. I have found that the throwing off of these ions by the electrodeis much more elfective with some materials than with others; and

2nd, p iment further shows that with ac the filament,

very suitable materials the ionization-is so rapid that a noticeableerosion of the electrode occurs. As this erosion is not uniform theelectrode usually made in the form of a filament (when made of a singlesubstance) soon becomes thinner and of higher electrical resistance atone spot. The result is that such eroded spot becomes the hottest part.of the filament and performs a largely increased share of its work asan electrode, leading to still greater erosion, and thus in a short timethe circuit through the filament is broken and the instrument rendereduseless.

By my invention, separating the heating functions from the detecting,rectifying, amplifying, or other electrodal functions of I select forthe heating function a material as, forinstance, tungsten, which hasqualities especially adapted to that function and looking to efficiencyand durability in heating, and I cause the heat thus generated to actupon another material (as for instance tantalum), which possesses in ahigh degree the physical, chemical or molecular properties required forthe said electrodal functions.

In the illustrated embodiment I have provided a tungsten filament Aconnected with platinum leads B which are sealed in the glass bulb, andthis tun sten filament performs the said heating auction. The substancewhich performs the said electrodal functions is, in the presentinstance, atantalum wire or ribbon C Wound around the tungstenfilament.. Where suitable salts of" the electrodal material areavailable, electroplating is a convenient method of applying the same tothe filament. Any convenient In the operation of my electrode, theerosion of the electrode is more uniformly distributed and does notaffect the heating function of the filament. The conductivity of'thetungsten filament is not materially altered by the erosion of anyportion of the tantalum wire, and the electrode will continue to performits two functions so long as any portion of the tantalum Wire is presentupon the electrode.

I claim:

1. An electrode of the class described, comprising a tungsten filamentand a covering of tantalum.

2. An electrode of the class described, comprising a filament adapted tobe heated electrically, and a covering of tantalum.

3. An electrode of the class described, comprising a tungsten filamentand a sheath of tantalum inclosing said filament.

In testimony that I claim the foregoing I have hereunto set my hand.

WALTER G. HUDSON.

Witnesses:

EDWIN J. PRINDLE, L. Bnonm'nom.

